FM Deviation Meter - Page 1
Forum section: electronics / testgear

author: jgalak
author_rank: Regular Contributor
timestamp: March 21, 2018, 11:08:50 pm
content: I would like to get an FM deviation meter that could be used for tuning transmitters in at least the 2m band, and preferably in the 70cm. (at the moment I'm trying to tune an APRS beacon, but I'm sure there'll be other uses)Unfortunately, I have never used one and know nothing about them. There's always a number of used ones on ebay, but I don't know what's worth getting. Something reasonably easy to use and not huge would be great (there are some vintage ones on eBaywith CRT scopes and tubes that appear to be enormous and difficult) . I'm fine with an older used one (though not one that would require a ton of TLC) or a new one, as long as it gave me reasonable results. Ability to go down to very low power levels would also be helpful.Price on the lower end (under $500? Better yet under $300 or so?) would be a big plus.I'd love a full-blown service monitor, but those are too expensive, even used.I've been using an RTL-SDR dongle to try to do this, but I spend so much time fighting the dongle I never know if an error is in the transmitter or in my failure to correctly use the software. Which is why I'd like a standalone unit.I'd appreciate recommendations for specific makes and models.Maybe something like this:https://www.ebay.com/itm/Marconi-Instruments-AM-FM-Modulation-Meter-ANALYZER-TF2300B/232488057811?epid=1624645396&hash=item36215e3bd3:g:jNwAAOSwi8xaQkK5? Though it still seems on the big side...Or maybe just an MFJ-224? Though I've never been a fan of MFJ products....

author: EE-digger
author_rank: Frequent Contributor
timestamp: March 22, 2018, 12:59:42 am
content: Don't forget you could also use a spectrum analyzer to get a good estimate. It would be interesting to see if a USB Spectrum analyzer (can be < $100) could pull it off. Ideally, you'd want "max hold" and "min hold" functions. There are numerous videos on ways of doing this, including some EEVBlog ones.

author: xrunner
author_rank: Super Contributor
timestamp: March 22, 2018, 01:21:41 am
content: If you can find a Heathkit IM-4180 they are reasonably accurate. Might be one for sale on Ebay. I have one and use it from time to time to set deviation on ham equipment.Here'a a thread I posted when I got mine for only $61 -https://www.eevblog.com/forum/rf-microwave/heathkit-im-4180-deviation-meter/

author: jgalak
author_rank: Regular Contributor
timestamp: March 22, 2018, 01:49:57 am
content: Quote from: EE-digger on March 22, 2018, 12:59:42 amA real Spec An is on my "to get" list, but that's a much bigger investment...

author: KE5FX
author_rank: Super Contributor
timestamp: March 22, 2018, 02:21:51 am
content: HP 8901As are going for less than $100. Could be a good option. (Sorry, model # corrected.)

author: David Hess
author_rank: Super Contributor
timestamp: March 22, 2018, 02:27:39 am
content: What I have done in the past is tap the FM demodulation output of a receiver which covers the bands that I want and calibrate it in Hz/Volt using an SSB receiver and FM transmitter to produce a known FM deviation using the Bessel method. A spectrum analyser which shows the sidebands of the FM signal can be used instead of an SSB receiver.

author: jgalak
author_rank: Regular Contributor
timestamp: March 22, 2018, 02:32:43 am
content: Quote from: KE5FX on March 22, 2018, 02:21:51 amWhere? They are $2K+ on eBay.

author: edavid
author_rank: Super Contributor
timestamp: March 22, 2018, 02:48:45 am
content: Quote from: jgalak on March 22, 2018, 02:32:43 amWell, the HP 8902A is not $2K if you look at actual sales, but he probably meant the HP 8901A. I don't like them, since they are huge, heavy, loud, and slow.What you really want is a Boonton 8210, but they are not as common as they used to be.Here's a recent sale:https://www.ebay.com/itm/Boonton-8210-Modulation-Meter-Working-Calibrated-HAM/292455096124

author: Performa01
author_rank: Super Contributor
timestamp: March 22, 2018, 06:03:47 am
content: Another vote for the Boonton 8210. Excellent device, compact and easy to operate.2MHz - 1.5GHzSelf-CalibratingAutomatic tuning and levellingTrue peak detection

author: Ringmodulator
author_rank: Regular Contributor
timestamp: March 22, 2018, 11:28:23 am
content: I would recommend a Racal Dana 9008.They are sold in the range of 120-190€ in the EU.(I own 2 of them).I am not sure about the availability in the US used market.

author: jgalak
author_rank: Regular Contributor
timestamp: March 22, 2018, 02:24:03 pm
content: Quote from: Performa01 on March 22, 2018, 06:03:47 amIs Boonton generally good? I've also been looking at their RF power meters,like the 4220. I want something that can measure low power - 100mW and down.

author: Performa01
author_rank: Super Contributor
timestamp: March 22, 2018, 02:50:34 pm
content: Quote from: jgalak on March 22, 2018, 02:24:03 pmWhat a coincidence! I have the Boonton 4210 with 18GHz sensor and it has always served me well. It does not have the fancy sensor interface with access to internal correction tables like more modern power meters do, but I still like it. The correction table is printed on the sensor and the correction factor has to be dialed in on the instrument manually - not a big deal for most applications, especially when they are always in the same narrow frequency range anyway.Boonton gear has been quite well regarded back in its days.BTW, many sensors can only handle 10mW maximum (but down to 1nW in exchange), but that isn't a problem, as it's nothing that an external in-line attenuator couldn't fix.

author: KE5FX
author_rank: Super Contributor
timestamp: March 22, 2018, 08:31:45 pm
content: Quote from: edavid on March 22, 2018, 02:48:45 amThey're huge, heavy, and loud, but what does "slow" mean? You feed it a signal and it tells you the deviation more or less immediately.

author: CJay
author_rank: Super Contributor
timestamp: March 22, 2018, 08:51:38 pm
content: Sayrosa, Wayne Kerr, RF Logic,Farnell AMM 257 (all the same thing and I think still made) is what sits on my bench, last cal date was back in the early 2000s and it still seems accurate if I use it to measure the deviation of a signal from the sig gen of my CMU200sCost me £65 plus shipping ($92 ish at current exchange rate) and can be had with GPIB, internal battery pack, auto locks to signals between 1.5MHz and 2GHz if you give it a short length of wire or, of course, you can plumb it in to a test bench.

author: w2aew
author_rank: Super Contributor
timestamp: March 22, 2018, 09:27:16 pm
content: I have both the Marconi TF-2304 and the Heathkit IM-4180. Both work pretty well. The Marconi will automatically tune to the carrier frequency, while you have to manually tune the Heathkit.As others have mentioned, you can also measure FM Deviation with a spectrum analyzer. I have a video on this (see below).You can also measure deviation without any special equipment using the Bessel Null method - I have a video on this too (see below again).

author: edavid
author_rank: Super Contributor
timestamp: March 22, 2018, 11:16:20 pm
content: Quote from: KE5FX on March 22, 2018, 08:31:45 pmI thought I remembered it as being rather sluggish in responding to the buttons and making measurements, but I haven't had one in years, so I could be wrong. Maybe I was just in a rush to get the measurement and turn the noisy thing off.

author: jgalak
author_rank: Regular Contributor
timestamp: March 23, 2018, 12:04:13 am
content: Quote from: w2aew on March 22, 2018, 09:27:16 pmYup, watched those videos, but not thrilled with the results I got, for various reasons. I don't have a SpecAn. Tried to use the technique you show using an RTL-SDR dongle as a "poor man's SpecAn", and got wacky results - and have no idea if the problem is the dongle, the transmitter, or, most likely, PEBCAK.I'm going to give the Bessel Null method a try next, using either the dongle or my handheld Yaeus radio (I don't currently own any other recievers that can handle 144MHz), but it's a little bit annoying since my transmitter isn't rigged to accept an arbitrary tone input, just the mark and space tones from APRS. (an obivous mistake that'll be fixed in the next revision of the PCB). So I need to bodge in a wire to let me connect my signal generator to the TX input.That's one of my issues - when both the transmitter and test equipment are jerry rigged, it's hard to tell if an unexpected result is a problem with one or the other....Which is why I want an actual meter that I can rely on, to rule out the test gear as the suspect.