A Front-panel view of my FT-817. 

My own testing and measurements:

Out-of-the box (and even after the so-called "MARS-CAP" mods) the receive frequency range (for the standard USA version) is as follows:

• 100 KHz to 56 MHz, continuous, all modes (except WFM, which is available only in the 76-108 MHz range.)
• 76-108 MHz, continuous, WFM only.  (Note that 76-88 MHz range in included because the FM broadcast band in Japan and some parts of Eastern Europe starts below 88 MHz.)
• 108-154 MHz, continuous, all modes (except WFM.)
• 420-470 MHz, continuous, all modes (except WFM.)

Cramming all of this capability into such a small box is really quite an amazing feat.  One should not, however, expect that such a small, relatively inexpensive radio will have receiver performance equal to the highest-end receivers out there.  When I read about people complaining of some relatively minor performance deficiency (such as noise blanker operation or the presence of birdies) then I have to refrain from dashing off an email reminding them that the FT-817 is not and was never intended to be the penultimate receiver.  Nevertheless, its performance is really very good in the amateur bands.

Soon after purchase I utilized several pieces of test equipment available to me (i.e. service monitors, etc.)  One of the first things that I did was to check the receiver sensitivity and image rejection on various frequencies - some aspects of which have not (to my knowledge) yet been reported elsewhere.

Note:  These measurements were performed on a factory-aligned FT-817 using the original configuration parameters.
 

Freq. (MHz)	SSB MDS	SSB S1	SSB S9	FM S1	FM S9	12db SINAD	20db SINAD	Image Rej. db
0.1	100	10000	174000	7000	36000	4000	8300	-
0.1 IPO	6.0	787	8100	450	2060	164	290	-
0.2	1.0	31	530	22	112	14	22	-
0.2 IPO	0.67	26	279	13.8	67.4	10	20	-
0.3	0.2	17.1	246	11.6	54.2	5.4	8.6	-
0.3 IPO	0.65	20.5	216	11.1	54	6.0	8.9	-
0.4	0.2	12.8	159	7.4	35	3.5	5.5	-
0.4 IPO	0.20	17.9	299	10.4	47	4.8	7.6	-
0.5	0.125	8.9	107	5.8	27	1.9	3.1	45
0.5 IPO	0.17	17.9	178	9.7	45	4.0	6.5	-
0.6	0.125	7.4	95	4.7	19.6	1.1	1.8	-
1.0	0.07	4.1	47.7	2.2	11.1	-	-	-
1.5	0.03	3	40	1.7	8.9	0.58	0.95	-
1.8	0.03	3.0	36.8	1.7	8.0	0.63	0.97	55
3.5	<0.03	2.3	29.1	1.4	6.4	0.87	1.25	-
7.0	<0.03	2.2	24.3	1.2	5.8	0.25	0.58	65
10.0	<0.03	2.0	22	1.2	4.9	0.29	0.48	64
14.0	<0.03	1.5	17	0.9	4.2	0.29	0.45	67
18.0	<0.03	1.5	16.7	0.9	4.2	0.27	0.46	-
21.0	<0.03	1.5	17.2	0.9	4.3	0.30	0.48	77
24.5	<0.03	1.5	16.2	0.83	4.1	0.28	0.43	-
28.0	<0.03	1.5	17.4	0.89	4.1	0.30	0.48	85
33.0(hf)	<0.03	3.1	34.5	1.7	8.5	0.3	0.6	89
33.0(vhf)	<0.03	0.8	8.6	0.4	2.1	0.15	0.25	90
44.0	<0.03	0.85	8.8	0.47	2.2	0.15	0.26	92
50.0	<0.03	1.5	10.4	0.54	2.6	0.31	0.57	100
56.0	<0.03	1.7	18.4	0.96	4.6	0.22	0.55	-
76.0	-	-	-	5.8	11.4	4.0	5.6	60
83.0	-	-	-	-	5.3	-	-	56
87.9	-	-	-	-	5.6	-	-	39
88.0	-	-	-	-	4.0	-	-	22
93.0	-	-	-	-	9	-	-	15
95.0	-	-	-	-	6.2	8.3	11.0	15
98.0	-	-	-	-	7.9	-	-	15
103.0	-	-	-	-	10	-	-	13
108 (wfm)	-	-	-	-	5.9	5.1	6.6	9
108 (air)	<0.03	6.0	65	3.8	16.7	0.81	1.8	>99
113.0	<0.03	2.8	25	1.5	7.1	0.35	0.58	-
121.0	<0.03	1.22	13.5	0.69	3.1	0.25	0.39	>114
137 (air)	<0.03	2.9	28	1.5	7.2	0.38	0.59	108
137 (2m)	<0.03	1.15	12	0.63	2.88	0.22	0.33	>108
144.0	<0.03	1.1	11.5	0.56	2.74	0.19	0.30	109
148.0	<0.03	1.0	9.6	0.51	2.44	0.20	0.30	111
154.0	<0.03	1.08	10.8	0.55	2.7	0.2	0.3	111
420.0	<0.03	1.85	20	1.12	5.38	0.33	0.54	60
430.0	<0.03	0.54	6.2	0.34	1.58	0.17	0.27	77
440.0	<0.03	0.57	6.5	0.35	1.69	0.17	0.27	82
450.0	<0.03	0.81	9.3	0.50	2.4	0.17	0.27	88
460.0	<0.03	2.8	29	1.63	7.6	0.35	0.56	80
470.0	0.04	9.4	100	5.5	25	1.0	1.72	65

A few notes about these measurements:

• All measurements were made via the front panel BNC connector
• All measurements were made using the standard SSB filter
• Note that when the "IPO" is off, the preamplifier is actually on.
• Blank entries indicate that readings were not taken as follows:
• At 1.0 MHz, 12 and 20 db SINAD readings weren't taken - because I forgot...
• In the FM broadcast band, the only mode available is WFM.  An "S1" reading was possible only at 76 MHz (see below.)  Also, more image/S meter readings were taken than SINAD measurements.
• Image response readings were not taken at all of the same frequencies as sensitivity readings, and vice-versa.
• Image response readings were taken with the IPO off (i.e. preamplifier on.)
• Except where "IPO" appears next to the frequency, all readings were taken with the IPO off (i.e. the preamplifier is on.)
• The "SSB MDS" column refers to "Minimum Discernible Signal" in the SSB mode.  In most cases, a CW signal was discernible at or below the 0.03 microvolt level (approximately -137 dbm.)  Because this is lower than expected antenna thermal noise under most conditions, readings were not taken at lower signal levels.
• Note that the 33.0, 108.0, and 137.0 MHz, readings were taken using two different frequency ranges which use two different RF circuits.
• For the "S1" and "S9" readings, the signal strength noted just at the point the appropriate LCD segments activate.
• At frequencies 1 MHz to 50 MHz, the gain of the preamplifier is nearly 10db.  With the preamplifier turned off (i.e. the IPO function is "on") the voltage sensitivity of the receiver decreases by a factor of 3.
• No significant difference in transceiver performance was noted between the front and rear antenna connectors.

Along with the radio's schematic, this chart can tell us a few interesting things:

• Below approximately 250 KHz, better receiver performance will be obtained if the preamplifier is turned off (i.e. the IPO is enabled.)  This is a result of the inductance of T1006 being inadequate at these frequencies.  The poor sensitivity at low frequencies with the preamp switched out (i.e. the IPO "on") is likely a result of the inadequate inductance at T1015 - the mixer input coupling transformer. (Note that L1002 and L1011, both 100 uH inductors, account for only few db at most as their reactance is over 60 ohms at 100KHz.)  It is unlikely that T1015 may be modified without adversely affecting performance at higher (VHF and UHF) frequencies.
• On most frequencies in the FM broadcast band, no input signal will result in an S1-S2 signal meter reading (on my '817, at least...)
• It should be noted that on 6 meters (i.e. 33-56 MHz) there are two preamplifiers in the receive path.  The first preamplifier (Q3019 on the final amplifier/filter board) is non-switchable.  There is, of course, the "IPO" preamp consisting of Q1008 and associated components that may be switched in and out.
• As is typical of most amateur gear, the S-meter readings on SSB, CW and AM are vastly different from those in FM mode.  This is because completely different circuits are used to derive these readings - even narrow FM and "wide" FM (WFM) use completely different circuits.
• In AM/SSB/CW/DIG mode, each "S" unit (at and below "10 over") corresponds to approximately 3 db on HF and on 2 meters and 70 cm, each "S" unit represents approximately 2 db.
• In the FM mode (not WFM) each S meter segment represents 1-2 db, depending on which segment is lit.  (Note:  Internally there are 16 levels of reading on the S meter but there are not that many segments, so one segment may represent more than one of these "levels" of reading.)

"What is Image Response?"

Every superheterodyne conversion scheme has what is called an image frequency.  Taking the FT-817 as an example, the first IF is at 68.33 MHz (except for the FM broadcast band, but more on this later.)  Whenever the 68.33 MHz IF is used, the local oscillator is always 68.33 MHz above the receive frequency:  When receiving at 10 MHz, the local oscillator is at 78.33 MHz, and for 440 MHz, the local oscillator is at 508.33 MHz.

There's also another false receiver response called an image.  If a filter were not used, our receiver (in the above example) would receive a signal at a frequency of twice the IF frequency (i.e. 136.66) MHz above the receive frequency.  Taking the example in the previous paragraph, this would mean that in addition to our 10 MHz signal, we'd receive something at 146.66 MHz, and in addition to our 440 MHz signal, we'd receive something at 576.66 MHz.

As you can see, having a fairly high first IF frequency - 68.33 MHz in our case - means that we need to filter out a signal that is 136.66 MHz away from where we want to listen.  If we had used an IF frequency of, say, 1 MHz, the image would be only 2 MHz away.  At AM broadcast band frequencies this sort of filtering isn't too hard to manage, but at 2 meters or 440 MHz, trying to filter a signal that is only 2 MHz away requires complicated and/or expensive filtering:  Filtering something that is over 136 MHz away is easy - even at 440 MHz. 

Even with filtering, that image still does exist - but is greatly reduced.  For clarity, here is a bit of explanation for the image response data on the chart:

• When the receiver is tuned to the lower frequency bands, the image is correspondingly lower in frequency as well.  This explains why, on the AM broadcast band, the image rejection is only 45db or so.  The image response is also worsened by the fact that the sensitivity on the AM band is somewhat worse than on higher frequencies:  The receiver's sensitivity drops off below 1 MHz or so, but it is quite good at much higher frequencies (i.e. at 137 MHz - where the image is.)  The FT-817 uses a diplexer (a filter-splitter) to separate the HF/6 meter signal from the 2 meter signals.  This has a low-pass response that, while adequate to keep the HF/6 meter signals out of each other's circuits, isn't at "full strength" just yet at 137 MHz.  Anyway, the "AM band" lowpass filter is used only when receiving on the AM broadcast band and the manufacturer had little reason to spend much money and go overboard with filtering - especially when the images land in a frequency range normally devoid of strong signals.
• The image response on 6 meters is better still.  This is mainly because the image is even farther above the lowpass portion of the HF/6 meter diplexer, allowing it to offer even better rejection.  There is also some fairly strong lowpass filtering involved.
• The 2 meter/aircraft receiver not only has a diplexer in it, but a 3-stage tracking front end.  This explains the excellent image performance.
• The 70cm receiver's receive frequencies are "closer" (percentage-wise) to the image than the other bands:  On 2 meters, the image is at almost twice the receive frequency, where on 70cm, the image is only 30 percent or so higher.  Also, the 70cm receiver uses a fairly broadband 3-stage helical resonator for most of its image rejection.  Even though it isn't as good as that on 2 meters, it is still really quite good.

On the FM broadcast band, the FT-817 doesn't use any of its high-dynamic range receive sections, but rather an all-in-one FM receiver chip - Q1025.  Furthermore, it uses an IF of only 10.7 MHz, so its image is only 21.4 MHz away.  Finally, its input filtering is rather minimal, using only the 2 meter diplexer and a single tracking filter.  In other words, there was little incentive to put more money than absolutely necessary toward FM broadcast band reception.

From 76 to below 88 MHz, the local oscillator (LO) operates on a frequency 10.7 MHz below that of the receive frequency, but from 88 through 108 MHz, the local oscillator operates 10.7 Mhz above the receive frequency:  This places the image 21.4 MHz below and above the receive frequencies, respectively.

Why the strange split?  Running the LO below the receive frequency below 88 MHz places the image in the 54-66 range - placing its image well into the diplexer's highpass filter cutoff frequency.  Running much higher than this with a low-side LO would reduce the filtering efficiency - right in the middle of the TV band, possibly resulting in hearing the buzz of TV carriers in that range.  Above 88 MHz, a high-side LO is used, placing the image in the range 109-129 MHz.  Even though the image response at 88 MHz and above is pretty terrible, all that is likely to be heard would be the occasional aircraft or airport transmission, and this would probably be much weaker than a high-powered FM broadcast station.

There is another problem with the FM receiver on the FT-817:  Using the "single chip receiver" has the advantage of low cost and simplicity.  Unfortunately, its dynamic range is pretty poor.  What this means is that the FM broadcast band receiver is very prone to strong signal overload - something that can't help but be noticed in strong signal urban areas - especially when using a large antenna.  It would have been nice if Yaesu could have routed that signal through a switchable attenuator for use in this frequency range, but...

"But the '817 can receive NOAA weather..." Yes, you can hear NOAA weather on your FT-817.  Simply tune in a frequency 136.66 MHz (2x the IF frequency) below your local (strongest) local NOAA frequency.  That is, 162.55 MHz would be tuned in at 25.890 MHz using FM.  The problem?  The filters in the '817 were designed to prevent this - because this is the image response.  The NOAA broadcast will be a mere 85 db weaker than it would be were the receiver designed to work at this frequency.  This means that your local NOAA broadcast must be really strong (i.e. you must be within a couple miles of the transmitter) for you to hear it this way - this is probably not going to work when you are backpacking... Now, if you want to work around this, you could do one of several things (and no, adding an 85 db gain preamp isn't one of them...):  Build an NOAA downconverter.  This is one of my projects that I am slowly working on.  Such a converter can be small and light, and simply attach to the BNC connector, for example. Get some of the antenna signal into the receiver.  Two possible "injection" points are:  At the mixer - the junction of C1117 and T1015.  Another is at the junction of T1006 and L1011 - a method contingent on the frequency response (and operation) of the HF preamp based on Q1008.  Note that both of these points are reachable on the top of the main board but the problem of doing these sorts of things that they must be done in a way to avoid seriously compromising radio performance - and trying to figure out how to get the antenna RF to these modifications.

IF rejection in the FT-817:

You may have already figured it out, but a superheterodyne is actually a single-frequency (the IF frequency) receiver with a converter in front of it to translate the receive frequency to the IF frequency.  It follows that it takes some care to keep signals on that IF frequency from getting into the receiver.  In the case of the FT-817, that means that a strong enough signal at 68.33 MHz will "break" through and you will hear it no matter where you tune the receiver.  The FT-817, therefore, has some filtering to keep that from happening.  The performance of this filtering is as follows:

• At HF frequencies (i.e. 1.8 through 28 MHz) the 1st IF rejection is approximately 100db - pretty good, actually...
• At 6 meters, the 1st IF rejection is approximately 85db.  Because 6 meters is "closer" to the 68.33 MHz IF frequency, the lowpass filtering present in the HF ranges isn't there to reduce it.  This rejection is still quite good.
• On the aircraft band, the 1st IF rejection is approximately 105db.
• On 2 meters, the 1st IF rejection is approximately 101db.
• On 70cm, the 1st IF rejection is approximately 110db
• The IF rejection on the FM broadcast band wasn't measured, but since the 10.7 MHz IF signal (for the WFM receiver) would have to get through the 6 meter diplexer, it is expected that it would be quite good.

The FT-817 actually has two IFs in it:  The 68.33 MHz IF is at a high frequency to simplify image filtering (as described above) but it is rather difficult and expensive to make a highly selective filter that operates at such a high frequency, so the filter that does operate there is fairly broad and only has mediocre selectivity.  To simplify filtering, the 68.33 MHz IF is converted down to 455 MHz (where we can get some good filtering at much lower cost) by mixing it with a 67.875 MHz signal - a frequency which happens to be exactly three times that of the master reference oscillator - a fact that is not a coincidence.

This IF has an image, too:  The 68.33 MHz IF filter is pretty narrow (10-20 KHz or so) but an image can occur that is 910 KHz (twice the 455 KHz IF) above the receive any frequency (except on the FM broadcast band.)  This means that if you are tuned to, say, 10 MHz, it is possible to hear a signal that is at 10.910 MHz.

But how well filtered is this?  As it turns out, the 68.33 MHz IF filter is able to attenuate this 2nd IF image such that it is 55db down.  This means that the signal 910 KHz above the current receive signal must be over 300,000 times as strong as the one you are tuned to in order to show up on the S meter with the same strength.  In actual operation, it is very unlikely that this image will cause you any problem, unless you have a next door neighbor that is operating exactly 910 KHz above where you are receiving.

This might then bring up the question:  "If some of the 68.33 Mhz 1st IF signal can get through, then can a 455 KHz signal get into the IF from the antenna?"  The answer is yes, it can.  This was noted only in the AM broadcast band and in the 1.8 range.  In the 1.8 MHz range, this "leakage" was down 95 db down.  The "leakage" was a bit greater in the AM broadcast band, but it was still very minimal.  Anyway, you'd need to have a very strong signal on 455 KHz in order for this to be any sort of problem - and that's not likely to happen - because there really aren't any!.

The Radio's Front End Filtering:

Front End filtering is one of several determining factors of receiver performance.  As is typical of most modern HF amateur transceivers, the receive bandpass is set by cascading the transmit lowpass filter with a highpass filter:  The highpass filter is switched out during transmit.

The coverage bands of the highpass/lowpass filters are set as follows:

• 100 KHz - <1.8 MHz (FIL1)  There is no highpass filter in this frequency range per se (only a 0.1 uf capacitor) but there is only a lowpass filter with a sharp cutoff above 2.5 MHz.  Unlike many radios, no attenuator is automatically switched in when tuning through the AM broadcast band.  This is evidenced from the schematic, as well as the fact that the attenuator is operational in this frequency range.
• 1.8 MHz - <3.4 MHz (FIL2)
• 3.4 MHz - <6.9 MHz (FIL3)
• 6.9 MHz - <13.9 MHz (FIL4)
• 13.9 MHz - <20.9 MHz (FIL5)
• 20.9 MHz - <33.0 MHz (FIL6)
• 33.0 MHz - 56.0 MHz (FIL7)  Note:  The lowpass filtering for 6 meters is provided by the HF/6meter diplexer.
• 76.0 MHz - 108.0 MHz (WFM Mode) and 108.0 MHz - 154.0 MHz (Aircraft and 2 meters.)
• 420.0 MHz - 470.0 MHz (70cm)

• A highpass filter (consisting of C3236, L3072, C3245, L3075, and C3254) passes only the UHF (70cm) energy.  A lowpass filter (consisting of C3076, L3028, C3082, L3032, C3088, L3035, and C3093) provides such filtering for 70cm.
• A lowpass/highpass network (consisting of C3264, L3081, C3265 for the lowpass filter and C3260, L3079, C3252, L3075, C3243, L3071, and C3234 for the highpass filter) separate the signals from 76 through 154 MHz from the HF/6 meter and UHF signals.
• A lowpass filter consisting of C3257, L3069, C3239, L3070, C3242, L3074, C3248, and L3077 removes signals above 56 MHz.
• A lowpass filter (on the main board) consisting of C1021, L1005, and C1022 that has a 3db cutoff frequency of approximately 80 MHz.
• For HF/6 meters, an IF-reject filter consisting of T1014, C1119, C1120, and R1103 blocks 68.33 MHz energy - which happens to be in the region of U.S TV channel 4.
• For FM broadcast, very broad filtering (consisting of the high/lowpass diplexer filtering mentioned above) as well a tracking filter consisting of varactor D1034, TC1003, and L1024 provides preselection.  Because of this minimal filtering, low-side LO injection is used from 76-88 MHz, and high-side LO injection is used from 88-108 MHz.  The image response in the frequency range is quite poor when receiving in the 88-108 range.
• For the 108-137 MHz range (aircraft) a 3-stage tracking filter/preamplifier (starting at T1001) provides excellent receive performance in this range.  For some reason, the purpose of this section is not mentioned on the schematic or in the service manual.  The performance of this receive section makes it an excellent receiver for use in hunting signals on the old (and abandoned - although some ELTs still have a short-range transmitter on this frequency) 121.5 MHz ELTs (Emergency Locator Transmitter) in downed aircraft - especially if it is appropriately used in AM and SSB/CW modes. 
  
• For the 137-154 MHz range (2 meters) a 3-stage tracking filter/preamplifer (starting at T1002 and virtually identical to the aircraft-band preselector) provides excellent performance.
• For the 420-470 MHz range (70cm) the receive filtering is much simpler, consisting of a very broadly resonant  tuning/matching network consisting of TC1001 and L1006, followed by a preamplifier and CV1001, a 3-pole helical filter.  Because it does not have a tracking filter, it is more susceptible to overload and intermod than on HF or 2 meters.

A note about 222 MHz:

It is a shame that Yaesu did not see fit to put 222 MHz coverage in this radio.  It would have required, probably, another $25-$35 of components (i.e. high/lowpass filters, maybe another VCO section, and another RF section for receive and transmit.)  It should also be noted that the broadband nature of the power amplifier makes it perfectly capable of operation at 222 MHz.

Not including the 222 is not all that surprising, however:  It would be legal to use only in the U.S.A. and relatively few people would find it useful.  It is, however, a chicken-and-egg problem:  The band isn't used much because equipment isn't readily available.  The equipment isn't readily available because relatively few people use it.  The band isn't used much because equipment isn't readily available.  The equipment isn't readily available because...
 

Go to The KA7OEI FT-817 "Front Page" - This is, well, the "front" page of the '817 pages here...

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