WTB A working AM/FM modulated RF Signal Generator. - Page 1
Forum section: electronics / general

author: Specmaster
author_rank: Super Contributor
timestamp: August 19, 2017, 10:31:50 pm
content: Hi Chaps, does anyone have a decent working RF signal generator that will cover the AM and FM radio bands with suitable modulation for both AM and FM that they don't really need anymore? Needs to in the UK of course and not a lot of money as I don't have a lot to spare these days since I retired, there's a huge gulf between the pension and what I used to earn lol.I have been buying some on Ebay that are supposed to sort of working but it seems that I'm throwing good money after bad all the time as many sellers on Ebay are shall we say, economical with the truth when it comes to describing their items.I don't need reference standard gear neither do I need (no space for it) large units like some of them seem to be, my bench is only a home office desk and shelves are only 24 and 32 deep. So if anyone can help me out, please PM me. I live in Essex so the closer the better really as I might be able to come collect it rather than posting it to me.

author: bd139
author_rank: Super Contributor
timestamp: August 19, 2017, 10:50:11 pm
content: I assume this is for radio alignment based on your requirements?Having done this on the cheap (until recently - phew!) I share your worries about buying kit on ebay.I did everything with a knackered old Heathkit counter (£20), a Chinese clone RF generator (Solex 150MHz - £30) and a diode probe (DIY £5) and DMM (£10). Didn't even get the scope out. FM modulation at 110MHz ceiling was off the books for me as that meant expensive synthesized generators and still does today but you can still peak the IF with a carrier generator only and measure the IF with the counter. You can hack the RF generator with a varactor diode for FM modulation if you really want but I haven't done it myself. Probably cheapest option - couple of quid!I could have got away without the counter but the RF generator was so far out of calibration it was a necessity.My bench is the top of a 2x2 Ikea Kallax so I sympathise with you.

author: Specmaster
author_rank: Super Contributor
timestamp: August 19, 2017, 11:41:49 pm
content: You assume correct, I too have been making do by cobbling bits together to try and resolve issues but it's not the same and you're never 100% certain that the radio is as good as it could be if you had the right kit available. I've been using a Tech 20D signal gen with only AM modulation and because the scale is way off, invested in a frequency counter which is a bit hit and miss since the sig gen cannot supply sufficient output voltage to drive it at all frequencies, plus the counter only goes upto 100Mhz. I have a new one coming that I'm assured does indeed work and goes upto 1.3Ghz and hopefully does as its claimed to do, so that should provide me with an accurate frequency control if I can pair it with a suitable sig gen I'm just about done apart from a centre zero VTVM meter, although I think I could use a scope for this aspect.

author: bd139
author_rank: Super Contributor
timestamp: August 19, 2017, 11:59:16 pm
content: Just a note with the 1.3GHz-ish counters. They tend to have a 50 ohm termination required as that's well into "scary transmission line territory" so you'll probably have two inputs, one a high impedance usually up to about 200MHz (if you are lucky) and a 50 ohm terminated one up to 1.3GHz. The terminated one requires more power to get it to count so you will most likely have to rely on the lower frequency input. They are usually ok with a 10X scope probe attached to the high impedance input if the level is above 10-20mV or so.However you may still have problems with the sign gen - those old ones have quite a high output impedance and low power output so it might still not be enough to drive it still with an IF can and counter attached. I had the same problems with my (relatively modern in comparison) transistor based Solex which was frustrating.I would, to save the above problems if you can:1. Fire up the generator and leave it for an hour (they drift like mad).2. Mark up the generator with a new scale measured by your counter with the common IFs you will use.3. Disconnect the counter and stick the generator at the desired IF.4. Use a 10x scope probe or VTVM with diode probe to peak each stage.A counter is a relatively new invention really. I think my father aligned them with a Heathkit VTVM and uncalibrated Heathkit RF-1 and did ok!

author: 2N3055
author_rank: Super Contributor
timestamp: August 20, 2017, 09:06:48 am
content: Maybe something like this... if it workshttp://www.ebay.co.uk/itm/Marconi-Signal-Generator-TF2015-i-10Mhz-to-512Mhz/202026998597?hash=item2f09bf5b45%3Ag%3ANNUAAOSwVbtZjFfe

author: bd139
author_rank: Super Contributor
timestamp: August 20, 2017, 09:12:43 am
content: That's no good for AM broadcast.Philips did a nice one, the PM5324 which did 100KHz to 110MHz FM and AM and had a wobbulator built in. Basically the one stop RF box. Can you get them now? Nope and if you could you'd have to fight me for it

author: Specmaster
author_rank: Super Contributor
timestamp: August 20, 2017, 09:44:21 am
content: Quote from: 2N3055 on August 20, 2017, 09:06:48 amYes thats the sort of size, but I think that one also requires a synthesizer TF2171 to partner with it, I've seen it before on Defpoms channel.

author: Specmaster
author_rank: Super Contributor
timestamp: August 20, 2017, 04:51:16 pm
content: Quote from: bd139 on August 20, 2017, 09:12:43 amYou're right, I do want it for normal AM and FM broadcasts and I've just discovered that the Marconi TF595A/5 which is a AM/FM generator actually does not cover normal AM broadcast bands as it kicks in at 1,500KhzShould have done my homework a bit more before buying it